#include <math.h>
#include <stdio.h>
//键盘输入三角形三边，求其面积
void main()
{
    float a,b,c,s,ss;
    printf("please enter 3 reals:");
    scanf("%f %f %f",&a,&b,&c);
    if( a + b <= c || a + c <= b || c + b <= a )
    {
        printf("Its not a triangle!");
    }
    else
    s=(a+b+c)/2;
    ss=sqrt(s*(s-a)*(s-b)*(s-c));
    printf("\nArea of the triangle is %6.2f:",ss);
}